This invention relates to on-premise voice and data communication systems.
The most natural form of human communication is by voice. Besides face-to-face conversations, telephone has been providing the inter-connections between parties at different locations and times. The original direct connections quickly gave way to the switching systems provided by telephone companies, which have evolved to be the most flexible routing facilities for modern communication.
As the capabilities of the station instruments diversified and the subscriber""s applications grew more sophisticated, additional routing locally became very desirable. Private Automatic Branch exchange (PABX) switching machines satisfied this need in business environment by assigning each station an xe2x80x9cextension numberxe2x80x9d. Connections are then set up with direct wirings from the PABX""s central switching unit, very much like the telephone company configuration.
A major hurdle in deploying PABX capabilities to residential or small office settings is that the wiring in these premises is very limited. For example, the existing wiring in many residential settings is limited to one pair. Adding new wiring for the purpose of service expansion discourages most of the would-be customers.
U.S. Pat. No. 5,596,631 resolved this limitation by introducing a station controller module that performs PABX functions with distributed architecture on single telephone line. It provides the routing capabilities of a PABX without requiring any addition or modification to the existing wiring. The basic architecture could be replicated for multi-line configurations. However, for a premise that was originally set up with a single pair of telephone wires, expanding to multiple line distributed PABX service would encounter the wiring limitation again.
Multiplexing voice traffic by digital technology to reduce facility requirement has been practiced for quite some time. Normally, it is set up for long distance transmission over dedicated facility that is well maintained by trained professionals. Such technology is not suited for customer premise environment whereby distance is fairly limited, while the wiring is characterized by random topology with wide range of medium quality. And, xe2x80x9cplug and playxe2x80x9d, xe2x80x9cno maintenancexe2x80x9d are key product requirements.
In recent years, the fast proliferation of Personal Computers (PCs) in workplaces, has created a similar need among the data equipments. Local Area Network (LAN) has been deployed to meet such demand. However, since LAN technology was developed primarily for business applications, its operation principles does not suit very well for residential situations, either.
The lately available Home Phoneline Networking (HPNxe2x80x94U.S. Pat. No. 5,696,790) technology capable of transmitting high speed digital signal over a single pair of traditional on-premise telephone wiring has made residential level LAN service feasible. By utilizing existing on-premise telephone wiring as transmission medium, a digital data bus can be established among communication nodes equipped with HPN technology based interface modules.
Although HPN provides data communication among multiple PCs, it does not address the voice communication need among PC""s human operators. This is due to the fundamental differences between voice and data communications:
Connections for human voice conversation are only established on demand. Dedicated facility is used and consistent service quality has to be maintained throughout a session. For example, it would not tolerate any degradation such as noise caused by random time delay in transmission.
Physical connections among data equipments, on the other hand, are continuously maintained even if there is no information to transmit. All terminals are constantly monitoring the communication medium. Information is broadcasted whenever any terminal has message to sent. Since there is no overall system coordination, collisions among data terminals are expected as a norm. Consequently, system throughput degrades proportional to traffic. However, such degradation due to collision can be tolerated by users because there is no definitive expectation of data transmission speed. Since data equipment is designed to transmit information in packets, it can easily deal with the need of re-transmission when a packet is not received by the destination party. It is clear that even HPN technology is still not compatible with voice communication requirements.
It is therefore the objectives of this invention to present a methodology of extending the single line distributed PABX concept to a multi-line service, to combine with data LAN operation so that a unified local area network is formed, while staying within the restrictions of limited physical interconnect facility.
Another goal of this invention is to maximize system performance by dynamic resource allocation between voice and data communications according to the usage.
Yet another objective of this disclosure is to maintain an interconnect system that is physically modular, so that it does not require special knowledge and skill to set up and to operate.
This document discloses a novel local communication system that is based on Frequency Division Multiplexing (FDM) technology to share the same physical medium with the external wide area communication service. The local system itself utilizes digital Time Division Multiplexing (TDM) technique to integrate two types of signals, voice conversations transported by Time Division Multiple Access (TDMA) protocol and data messages transported by Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, into one unified local network.
The TDM technology transports voice traffic in an orderly designated time slot fashion. However, all time slots in a traditional TDM system are continuously xe2x80x9cusedxe2x80x9d even when there is no traffic to carry. If such xe2x80x9cemptyxe2x80x9d time slots are consolidated into one block of contiguous time interval, it is then possible to allocate it to data terminals which operate in on-demand random-access, and collision-avoidance mode. This operation architecture can therefore merge both voice and data applications into one uniform system with dynamic resource allocation. In other words, this is a communication system that its primary goal is to provide voice communication. Under such a precondition, the system would constantly allocate as much resources for data terminals as available.
One basic application for this methodology is to establish simultaneous voice PABX and data LAN services in residential and SOHO (Small Office Home Office) environments where very limited transmission facility, such as one single pair of telephone wires, has been hindering the deployment of modern communication services.
HPN technology is used as an example vehicle to demonstrate how to extend multi-line telephone company services to individual stations, to establish intercom among the stations, and to provide data networking among computing terminals, all on a single pair of telephone wires. Thus, the connection medium needed in a multi-line PABX based on U.S. Pat. No. 5,596,631 can be reduced back to only one physical cable. Simultaneously, the data terminals perform their services by utilizing the remaining resources not occupied by voice traffic.
One of the advantages of the present invention is that the size of the system would be rather flexible. When all telephone services are in standby state, the entire system resources can be used for data networking. At the other extreme, the system could be fully loaded with voice traffic, while the data traffic is slowed down for the corresponding duration of time. By setting a limit on the maximum number of simultaneous voice channels allowed, minimum data networking speed is guaranteed, while the voice traffic may experience congestions during peak usage. So, this system will be suitable for a wide range of situations, from isolated island of local intercom with or without data networking, single line residential home, through SOHO, to well established small business.
Conventional digitized voice requires 64 Kb/s (Kilo-bits per second) digital signal to represent. The HPN technology is currently offering 1 Mb/s (Mega-bits per second) data throughput. Therefore, it is capable of carrying traffic of about 15 talkers (or, over 7 pairs of conversations). With the projected 10 Mb/s and even faster transmission speed in the next generation HPN devices, several tens of voice conversations and a large number of data terminals can share one single pair of telephone line.
On the other hand, if compression techniques are applied to speech signals, the portion of the system time required by voice traffic can be reduced correspondingly. Therefore, higher percentage of system resources will be available for data transmission.